Lightweight portable heating device

ABSTRACT

A lightweight portable heating device consisting of a container assembly and lid assembly that house a tub assembly for the purpose of heating liquids and food submerged in aforementioned liquids by means of a multi-fuel burner. Container assembly provides for several structures that improve ergonomics and handling of the lightweight portable heating device. For instance, container assembly includes an integrated handle that surrounds the container assembly proximate the top portion of the container assembly and is molded into the container assembly. Integrated handle allows for the ease of moving of the lightweight portable heating device by personnel. Proximate the bottom of container assembly are lifting handles that enable the lifting of the device above shoulder level while also functioning as a tie down point.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

This invention was made with government support under Contract No.W911QY-18-9-0017 awarded by the United States Department of the Army.The government has certain rights in the invention.

BACKGROUND

The present invention is directed to tray ration heating systems (TRHS).Particularly, the present invention is concerned with a new and improvedtray ration heater (TRH) that takes advantage of modern components andmanufacturing techniques.

Army and Marine Corps mobile field feeding systems provide a method toprepare solider rations through the use of heavy fuel burner integratedappliances. A major element of several field feeding systems, such asthe Army Assault Kitchen (AK), is the TRH, which uses a heavy-fuelburner to prepare Unitized Group Ration Heat & Serve (UGR H&S) traypacks. The prior art TRH can heat up to 18 tray packs, which can feed upto 250 persons, by heating 30 gallons of water to a temperature between180-200° F. The same water can be used multiple times between cleaning,and the prior art TRH can heat water while on the move, making the priorart TRH a critical appliance for group ration preparation.

Although the TRH provides critical functionality to the services forfield feeding, the legacy unit has several deficiencies that limitfurther employment. Specifically, the weight, maneuverability, andmaintainability leave considerable room for improvement. For instance,the prior art TRH weighs 285 lbs. empty or 400 lbs. when loaded withmeals (18 UGRs with rack) and water (30 gal). The legacy TRH isconstructed of heavy-gauge stainless steel. Because of its weight, theTRH is a four-man lift (per MIL STD 1472 F) and is awkward to carry andmaneuver into the cargo bed of the HMMWV given the placement of thehandles. The legacy unit also has low efficiency, requiring longerheating times and greater fuel consumption. Our improved configurationresults in improved efficiency and shorter heating times.

For the foregoing reasons, there is a need for a new and improved TRHthat is superior thermal efficiency, lightweight, and highlymaneuverable.

SUMMARY

The new and improved TRH is a lightweight portable heating deviceconsisting of a container assembly and lid assembly that house a tubassembly for the purpose of heating liquids and food submerged inaforementioned liquids by means of a multi-fuel burner. Although thecontainer assembly can be manufactured through a variety of methods, thenew and improved TRH uses Rotational Molding (rotomolding) manufacturingtechniques that enable the fabrication of the container with all thecritical features from a polymeric material.

The container assembly houses the tub assembly and the mounting pointfor the burner box assembly, while a lid assembly will cover the tubassembly and is latched to the container assembly using latches. Thecontainer assembly provides for several structures that improveergonomics and handling of the new and improved TRH. For example, thecontainer assembly includes one or more integrated handles that surroundthe container assembly proximate the top portion of the containerassembly and these handles are molded into the container assembly. Theintegrated handle allows for the ease of moving of the new and improvedTRH by personnel. Proximate the bottom of container assembly are liftinghandles. Lifting handles are preferably made from metal and enable thelifting of the new and improved TRH above shoulder level while alsofunctioning as a tie down point. Further lifting handles can be maderemovable. In addition the new and improved TRH has skids, which canalso be removable and/or replaceable, attached at the bottom of thecontainer to protect the base of the unit from wear and allow for easypush/drag of the new and improved TRH along a multitude of terrain andsurfaces.

The tub assembly of the new and improved TRH includes a combustorsection, plural totally-submerged combustion byproduct flow passages, afirst turning manifold, a second turning manifold, an exit manifold, andan exhaust port. The combustion byproducts exit the combustion sectionand enter a center set of parallel flow passages that guide thecombustion byproducts towards the first turning manifold. The firstturning manifold combines the combustion byproducts from the center setof flow passages and allows the combustion byproducts to turn around andenter the second set of intermediate combustion byproducts flow passagesto travel towards the second turning manifold located on the oppositeside near the entrance of the combustor section. Upon arrival at thesecond turning manifold, the combustion byproducts from the intermediateflow passage section once again recombines, turns around, enters theouter set of final flow passages and travels towards the exit plenum.The exit plenum combines the flow from the outer set of flow passagesand redirects it towards the exhaust port where the combustionbyproducts exit the new and improved TRH.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other features, aspects, and advantages of the presentinvention will become better understood with regard to the followingdescription, appended claims, and accompanying drawings where:

FIG. 1 shows a perspective view of the top, front, and right side of thelightweight portable heating device.

FIG. 2 shows a perspective view of the container assembly with cutawaysand the lid removed.

FIG. 3 shows a perspective and cut away view of the tub assembly for thelightweight portable heating device.

FIG. 4 shows a schematic representation of the flow path of combustionbyproducts through the piping.

FIG. 5 shows a perspective view of the piping within the tub assemblyand a perspective view of the path of the combustion byproducts throughthe piping.

FIG. 6 shows a perspective view of the bottom side of the lid assemblyfor the lightweight portable heating device.

FIG. 7 shows an exploded view of the burner assembly for the lightweightportable heating device.

FIG. 8 shows a perspective view of the bottom, rear, and left side ofthe lightweight portable heating device.

FIG. 9 is an exploded view showing the various components and assembliesof the lightweight portable heating device.

FIG. 10 shows a support structure assembly that is contained within thecontainer assembly.

DESCRIPTION

In the Summary above and the Description, and the claims below, and inthe accompany drawings, reference is made to particular features(including method steps) of the invention. It is to be understood thatthe disclosure of the invention in this specification includes allpossible combinations of such particular features. For example, where aparticular aspect or embodiment of the invention, or a particular claim,that feature can also be used, to the extent possible, in combinationwith and/or in the context of the other particular aspects andembodiments of the invention, and in the invention generally.

In FIG. 1 , the lightweight portable heating device 10 consists of acontainer assembly 20 and lid assembly 30 that house a tub assembly 40,see FIGS. 3 and 8 , for the purpose of heating liquids and foodsubmerged in aforementioned liquids by means of a burner 320, see FIG. 7. Although the container assembly 20 can be manufactured through avariety of methods, the present embodiment uses rotomoldingmanufacturing techniques that enable the fabrication of the containerwith all the critical and beneficial features from a polymeric material.As shown in FIG. 2 , a support structure assembly 70, see FIG. 10 , canbe inserted into the mold cavity such that once the container assemblyis rotomolded, the support structure 70 will be completely encapsulatedwithin, thereby strengthening the container assembly 20 and transferloads through the support structure assembly 70 rather than thecontainer assembly 20. As shown in FIG. 10 , the support structureassembly has flanges 72 on the ends and threaded inserts 74 that willaccommodate the lifting handles 80 which will be discussed below.

The container assembly 20 houses the tub assembly 40 within its fourwalls, acts as the anchor for the lid assembly 30, and the mountingpoint for the burner box assembly 50. In addition, container assembly 20provides for several structures that improve ergonomics and handling ofthe portable heating device 10. As shown in FIGS. 1 and 2 , containerassembly 20 includes an integrated handle 60 that is attached to thefour walls and surrounds the container assembly 20 proximate the topportion of the container assembly 20 and is molded into the containerassembly. Integrated handle 60 allows for the ease of moving of thelightweight portable heating device 10 by personnel. Integrated handle60 is contoured, along with container assembly 20 to permit the ease ofhands with bulky gloves to grab hold of the integrated handle 60.Proximate the bottom of container assembly 20 are lifting handles 80that are attached to each side wall. Lifting handles are preferably madefrom metal and enable the lifting of the lightweight portable heatingdevice 10 above shoulder level while also functioning as a tie downpoint. Further lifting handles 80 can be made removable. The liftinghandles may be attached to the container assembly by threaded fasters(not shown) that would thread into the thread inserts 74 on the flanges72 attached to the support structure assembly 70. As shown in FIG. 8 ,skids 90 attached at the bottom of the container to allow for easypush/drag of the lightweight portable heating device 10 along amultitude of terrain and surfaces. Skids 90 can be made removable sothat they can be replaced when worn out due to scraping over rough orabrasive terrain. The skids can also be replaced with wheel assembles(not shown) to allow transport over paved surfaces. In addition, theskids can be removed and the skid mounting fixtures used to secure theimproved TRH to a structure such as a truck bed or ship surface (notshown).

As best shown in FIG. 2 , container assembly 20 has a number ofadditional features. Integrated container hinge 100 will connect withcomplementary integrated lid hinge 115 (FIG. 6 ) on lid assembly 30. Theinterior of the container assembly 20 includes an integrated shelf 110for supporting the tub assembly 40 especially when the tub assembly 40is filled with liquid. On the exterior of container assembly 20 areintegrated support structures 120. Integrated support structure 120provide additional support and rigidity to the lightweight portableheating device 10 without adding a substantial increase in weight. Theintegrated support structure smoothly tapers into the sidewall of thecontainer subassembly 20 to avoid any potential snagging points oredges. In addition, integrated support structures 120 located on theside walls provide additional strength to the integrated handle 60 thatsurrounds the container assembly 20. Throughout the exterior andinterior surfaces of the container assembly 20, threaded inserts 130have been molded into the structure and are positioned at strategicpoints in order to secure other essential and optional components forthe lightweight portable heating device 10. Access holes 140 located inboth the first and second end walls are molded into the containerassembly 20 and are used to insert equipment needed for the distributionof combustion byproducts through the lightweight portable device 10. Theinternal cavity of the rotomolded assembly container 20 may beoptionally filled with foam 150 for the purposes of providing thermalinsulation, noise insulation, increasing rigidity, and providing overallstrength to the container. There are many types of foams that can beused, some providing better stiffness or crush resistance white othersproviding better insulative or buoyancy benefits. As a minimum,polyurethane, polystyrene, syntactic, and polyethylene foams can be usedindividually or combined in the internal cavities of the rotomolded tuband cover.

FIG. 3 illustrates the tub assembly 40 that fits inside the containerassembly 20. The tub assembly 40 is a metal structure that isessentially four walls and a base that contains the liquid to be heatedand hot combustion product flow passages (piping or tubing) 170 throughwhich hot combustion byproducts from the burner can flow in order totransfer heat to the liquid present within the tub assembly 40. In thisembodiment, the tub assembly 40 is manufactured from stainless steelsince it offers a hygienic, non-corrosive material option to be usedwith most common materials that can also sustain the elevatedtemperatures from the combustion byproducts. As shown in FIG. 3 , thetub assembly 40 consists of a combustion gas chamber section 160, flowpassages 170 located in the base of the tub assembly 40 and run parallelto the side walls of the tub assembly 40, manifold dividing bulkhead180, a first turning manifold 190, a second turning manifold 200, exitmanifold 210, exhaust port 220, shelf 230, drain 240, probe support 250,and sensor mount 260. The combustion gas chamber section 160 serves tocontain the burner's 320 flame coming from the burner box 50, afterwhich combustion byproducts will enter the seven first-pass combustionbyproduct flow passages 170A (see FIGS. 4 and 5 ) that are in contactwith the liquid within the tub assembly 40 in order to heat up theliquid. Since the combustor section 160 and flow passages 170 aresubmerged within the fluid and completely surrounded by the fluid inthis design, the maximum temperatures of these components are exposed tois somewhat limited by the boiling point of the fluid, thereby allowingthe use of widely available, lower cost metal materials such asstainless steel rather than exotic superalloy alternatives such asHastelloy.

As shown in FIG. 4 , the flow passages are comprised of multiple seriespasses through the liquid located in the tub 40 and starting with theintake manifold 165 that distributes the combustion byproducts withinthe combustion gas chamber section 160 into the first set of parallelflow passages 170A. In this parallel-series flow configuration (ourcurrently preferred embodiment), there are three passes, the first groupof seven parallel flow passages 170A (four being shown to avoidcomplexity in the FIG. 4 ) being submerged in the liquid and locatedin-between the combustor outlet and the first turning manifold 190 inthe center region of the tub base. The first turning manifold 190 thenturns the flow from these seven initial passages and redirects the hotcombustion gas byproducts back through the liquid region (second pass)of the tub via the second group of six parallel combustion passages170B, where three combustion flow passages are located on each side ofthe initial first pass of seven passages. The second turning manifold200 then creates a third pass through the liquid by turning the flowfrom these six parallel flow passages and redirects the combustion gasbyproducts back through the liquid region of the tub via the third groupof six parallel combustion passages 170C, where three passages arelocated on each side of the second pass passages. The combustionbyproduct gasses then exit these six tubes and are recombined in theexit manifold 210 and directed to the exhaust port 220 by the exitmanifold 210. In this embodiment, to reduce manufacturing costs andsimplify assembly the first and exit manifolds are manufactured as asingle integrated manifold and bulkheads 180 are secured to this singlemanifold and the bulkheads 180 are used to separate the flow in thefirst turning manifold 190 from the flow in the exit manifold 210 thattravels up to the exhaust port 220.

It is well known in the art to design parallel, series, or combinationsof parallel and series flow paths in a heat exchanger, such as a shelland tube heat exchanger, and therefore it is to be understood that whilethree passes of the combustion products through the liquid with sevenparallel passages in the first pass and six parallel passages in thesecond and third passes has been described, other parallel and seriesflow combinations can be utilized.

FIG. 5 illustrates the inventive transfer of combustion byproductsthrough the tub assembly 40 to increase surface area and minimize heatlosses to ambient, thereby improving thermal efficiency and allowing useof lightweight lower melting point insulation and construction materialnot contemplated within the prior art. This unique design assures thatthe wall temperatures of the flow passages are kept from being extremelyhigh because theses passages are completely surrounded by the fluidbeing heated and the fluid's temperature is limited to the boiling pointof the fluid. This allows the use of less expensive and moreconventional metals, such as stainless steel or aluminum, instead ofexotic alloys, such as Hastelloy. Also since the heat released from thecombustion byproducts is essentially all directed into the fluid in thetub, the exterior shell of the container subassembly can be made of lowmelting point materials including plastics, such as rotomolded plastic,instead of metal.

As shown in FIG. 5 , the combustion byproducts enter the tub assembly 40through the combustion gas chamber section 160 and travel through intakemanifold 165 to enter into the combustion gas flow passages 170A locatedin the center portion of the lower section of the tub assembly 40 untilreaching the first turning manifold 190 located opposite of thecombustion gas chamber section 160. The first turning manifold 190forces the combustion byproducts to turn into a second set of combustiongas flow passages 170B that are also in contact with the liquid in thetub assembly 40. Once the combustion byproducts reach the second turningmanifold 200 which is proximate to the combustion gas chamber section160, the combustion byproducts once again are turned, by the secondturning manifold 200, into a third set of combustion gas flow passages170C that terminate at the exit manifold 210 prior to exiting throughthe exhaust port 220. To reduce manufacturing and assembly costs, thefirst manifold and exit manifold (which are both located on the sameside of the tub) are fabricated as a single manifold chamber and aninternal bulkhead 180 then divides this volume into two distinctmanifold chambers.

To better explain, the combustion byproducts exit the combustion gaschamber section 160 and enter the center set of seven individuallysubmerged combustion byproduct flow passages 170A that guide thecombustion byproduct towards the first turning manifold 190. Theinternal bulkhead 180 delineates the first turning manifold 190 from theexit manifold 210 to ensure the combustion gas byproducts flow from thecenter seven individual flow passages 170A only returns through the sixintermediate submerged flow passages 170B. The first turning manifold190 combines the combustion byproducts from the center set of flowpassages 170A and allows the combustion byproducts to turn around andenter the next set of six intermediate flow passages 170B (located threepassages on each side of the seven center passages 170A) to traveltowards the second turning manifold 200 located on the opposite sidenear the entrance of the combustion gas chamber section 160. Uponarrival at the second turning manifold 200, the combustion byproductsfrom the intermediate passages 170B once again recombine, turn around,and are directed to flow into the outer set of six final passages 170Cand travels towards the exit manifold 210. The exit manifold 210combines the flow from the outer set of six final passages 170C andredirects it towards the exhaust port 220 where the combustionbyproducts exit the lightweight portable heating device 10. As statedpreviously, while this embodiment has described a three series flow patharrangement with seven parallel passages in the first pass and sixparallel flow passages in the second and third passages, any number ofparallel-series flow combinations could be accommodated in thisinvention.

It should be noted that although this particular design uses manifoldsin which the combustion byproducts incoming from discrete tubularpassageways are combined prior to once again being discretized intoexiting tubular passageways, it should be noted in lieu of a manifolds,individual passageways that are bent at multiple locations can achievethe same objective; specifically, to guide the combustion byproducts totravel back and forth within the tub assembly 40 through submergedpassageways, that are completely encapsulated by the surrounding liquid,thereby increasing the residence time of the combustion byproducts andincreasing the surface area in contact with both the hot combustionbyproducts and water to increase the heat transfer delivered. Forexample, six individual tubes or passages that were each bent at 180degrees at two separate locations would effectively achieve the sameresult as the aforementioned design. Likewise, more numerous, smallertubular passageways with other bends could also be used to generate amore tortuous path and increase heat transfer surface area.

Returning to FIG. 3 , the tub assembly 40 features incorporates a tubshelf 230 designed to rest on the container assembly's 20 integratedshelf 110 in order to partially support the weight of the tub and liquidwithin. While the current embodiment uses a single support shelf orledge in the tub to rest on a corresponding shelf or ledge on thecontainer assembly, it is of course understood that additional shelflikeledges could be employed for additional support and/or the shelf orshelves could be asymmetrically located to assure the tub cannot beimproperly located into the container assembly. The drain 240 is locatedat the lowest location within the tub assembly 40 to enable completedischarge of fluid. A probe support 250 allows installation of the waterlevel probe (not shown in FIG. 3 ) and a sensor mount 260 allowsattachment of the thermostat or other temperature measuring device suchas a thermocouple, RTD, thermistor and the like (also not shown in FIG.3 ).

The lid assembly 30 has a number of features and those features are bestshown in FIG. 6 . The lid assembly 30, which is envisioned to berotomolded, and foam filled, features integrated lid handle 270,integrated lid hinge 115, integrated lid support structure 280,integrated lid vent 290, and integrated lid gasket track 300. Theintegrated lid handle assists personnel to open the lid assembly 30. Theintegrated lid support structure 280 provides additional rigidity to thelid assembly 30. Integrated lid vent 290 provides a pressure vent toprevent a buildup of pressure within the tub assembly 30 when the fluidinside the tub assembly 30 is heated. The integrated lid hinge gaskettrack 300 holds a lid gasket 310 in order to provide a seal between thelid assembly 30 and the container assembly 20. Mold-in threaded inserts130 can also be included during the rotomolding process to enableattachment of other parts or subassemblies. The internal cavity of therotomolded lid may be optionally filled with foam (not shown) for thepurposes of providing thermal insulation, noise insulation, increasingrigidity, and providing overall strength to the lid. As stated earlierwhen discussing foam filling the internal cavity created between thecontainer assembly 20 and the tub assembly 40, there are many types offoams that can be used, some providing better stiffness or crushresistance white others providing better insulative or buoyancybenefits. As a minimum, polyurethane, polystyrene, syntactic andpolyethylene foams can be used individually or combined in the internalcavities of the rotomolded tub and cover.

While the container assembly 20 is shielded from hot water due to theinsulation and air spaces between the tub assembly 40 and the containerassembly 20, the inside of the lid assembly 30 is exposed to convectiveand radiative heat transfer from the heated liquid in the tub. In onepreferred embodiment, the container assembly rotational molding processutilizes a low-temperature melting point plastic, such at Low DensityPolyethylene (LDPE) but the lid assembly 30 rotational molded part usesa higher melting point plastic, such as High Density Polyethylene.

FIG. 7 illustrates the burner box assembly 50. A burner 320 is housedwithin a burner box assembly 50 that protects the burner from rain anddirect contact. The burner box assembly 50 consists of a burner box 330and burner cover 340 attached by means of a burner cover hinge 350. Theburner cover features a burner cover access 360 to allow interfacingwith burner 320 without the need to open the burner cover 340. A latchbracket 370 and a latch 380 are mounted to the burner box 330 and burnercover 340 to ensure the cover remains in place during transportation andhandling. A multitude of different burner adaptor plates 390 that accepta variety of different burner configurations 320 may be used toconfigure the burner box to accept a particular burner type installedwithin the burner box assembly 50 with each burner adaptor platedesigned to accept the specific burner diameter, and burner mountingrequirements. A combustor flange 400 can be secured to the burner boxassembly 50 in order to prevent the flame and hot combustion byproductsfrom coming into unintended contact with the container assembly 20 orburning box assembly 50. A burner gasket 410 and a combustor gasket 420prevent hot air from bypassing the combustor flange.

As further shown in FIG. 7 , the burner box assembly 50 contains anelectronic compartment 430 protected from the elements by an electronicscover 440. The electronic compartment 430 houses an electrical connector450, breaker 460, and power switch 470 that are user accessible from theoutside of the burner box assembly 50. Within the electricalcompartment, there is a tilt switch 480 attached to a tilt switchbracket 490, a water level switch 500 connected to a water level probe510, and a thermostat 520. The tilt switch 480 prevents unsafe operationof burner 320 when lightweight portable heating device 10 exceeds apredetermined tilt angle. The water level switch 500 prevents unsafeoperation of burner 320 when liquid level is below the water level probe510. The thermostat 520 prevents unsafe operation of the burner 320 whenthe liquid temperature is outside an acceptable range. A terminal strip530 facilitates wiring among electronic components. An instrumentationgasket 540 located between the burner box 330 and container assembly 20prevents the intrusion of water into the electrical compartment 430.

As shown in FIG. 8 , drain plumbing 550 underneath the tub assembly'sdrain passes through the container assembly 20 to allow attachment of adrain valve 560 with standard plumbing connections. Also shown in FIG. 8are skids 90 that can be made removable. These skids can be replacedwhen worn out due to the unit being slid across rough terrain. Notshown, but contemplated within the scope of the invention, are the wheelassemblies or hard mounting brackets that can be installed in place ofthe removable skids.

FIG. 9 provides a perspective exploded view of a number of componentsthat constitute the lightweight portable heater device 10. A removablewire tray 570 can support a variety of enclosed food items (e.g.military's Unitary Group Rations (UGRs)) (not shown) with adequatespacing for proper heating. A removable screen 580 ensures that no foodor foreign object of any kind will restrict the convective liquid flowaround the combustion gas passages 170 or foul the exterior surfaces ofthe combustion gas passages. The removable screen also ensures that anysediment or debris is collected on the surface of the screen therebyallowing these deposits to be easily removed and properly disposed.Latch 35 secures the lid assembly 30 to the container assembly 20.

Also shown in FIG. 9 is an exhaust assembly that includes an exhausttube 590 and exhaust container gasket 610 that prevents the exhaust gasfrom overheating the low melting point plastic of the containersubassembly. Also shown in FIG. 9 is an exhaust tub gasket 600 thatattaches to the tub assembly's exhaust port 220 to redirect exhaustgases out of the lightweight portable device 10. The exhaust tub gasket600 also prevents gases from bypassing the exhaust tube 590. The exhausttube 590 and exhaust container gasket 610 are centered in the opening inthe container in order to provide an air gap to prevent overheating ofthe container plastic and are secured in place by means of an exhaustplate 620, which also prevents external rain or other objects fromingress into the container subassembly.

As further shown in FIG. 9 , a tub gasket 630 placed between the tubassembly and container assembly prevents water ingress into thecontainer subassembly's cavity. A compressible foam 640, located at theexhaust of the tub assembly between the tub assembly 30 and containerassembly 20, provides a restoring force that pushes and seals thecombustion gas chamber section 160 against the combustor flange 400 andaccompanying combustor gasket 420 to prevent leakage of hot combustionbyproducts.

It is understood that the described embodiment of totally submerging thecombustion gas passages 170 and using a total of 19 combustion gaspassages in three passes, with the first pass using seven passages 170Aand the remaining two passes 170B & 170C using six parallel passageseach has reduced the exhaust temperature to the point where centeringthe exhaust tube along with using the exhaust gaskets 600 and 610 on thetub and the container have been shown to be sufficient to prevent theoverheating of the plastic tub material in the region surrounding theexhaust tube. However, should the exhaust gas temperature become muchhigher, (or the selection of a lower melting point plastic), where thehigher exhaust gas temperature is a result of some change such asreduced heat transfer from the combustion gas passages or use of a lessefficient burner it is to be understood, that the region surrounding theexhaust tube could be insulated with a high temperature insulation, or aceramic liner (or other techniques well known in the art) to shield therotationally molded plastic from these higher temperatures.

The described versions of the present invention have many advantagesincluding improved heat transfer, improved ergonomics, reducedmanufacturing cost, simplified maintenance, reduced noise, reducedvibration and reduced weight.

While we have shown and described several embodiments in accordance withour invention, it should be understood that the same is susceptible tofurther changes and modifications without departing from the scope ofour invention. Therefore, we do not want to be limited to the detailsshown and described herein but intend to cover all such changes andmodifications as are encompassed by the scope of the appended claims.

What is claimed is:
 1. A tub assembly for a portable heating device,comprising: a first end wall; a second end wall and the second end wallis opposite the first end wall; an exit manifold proximate the secondend wall; a bulkhead extending between the second end wall and the exitmanifold; a first turning manifold proximate the second end wall; thebulkhead separates the exit manifold and the first turning manifold; asecond turning manifold proximate the first end wall; a first side walland a second side wall connecting the first end wall and the second endwall; a base connected to the first end wall, second end wall, firstside wall, and second side wall, and the first turning manifold and thesecond turning manifold are positioned in the base; and a plurality ofpassages positioned in the base to run parallel to the first side walland second side wall and the plurality of passages having end openingsthat extend into the first turning manifold and second turning manifold;a combustion gas chamber section in the base and adjacent the first endwall; wherein the plurality of passages comprises a first group ofparallel flow passages extending from the combustion gas chamber sectionto the first turning manifold and directing hot combustion gasbyproducts from the combustion gas chamber section to the first turningmanifold, a second group of parallel flow passages extending from thefirst turning manifold to the second turning manifold and directing hotcombustion gas byproducts from the first turning manifold to the secondturning manifold, and a third group of parallel flow passages extendingfrom the second turning manifold to the exit manifold and directing hotcombustion gas byproducts from the second turning manifold to the exitmanifold.
 2. The tub assembly of claim 1, further comprising: an exhaustport, whereby the hot combustion gas byproduct travel from the exitmanifold through the exhaust port and exit the tub assembly.
 3. Aportable heating device comprising: a container assembly having anexterior surface and an interior surface, at least one container hingealong a top edge of the container assembly and attached to the exteriorsurface, an integrated handle positioned proximate the top edge of thecontainer assembly and molded as part of the exterior surface,integrated support structures molded on the exterior surface and moldedinto the integrated handle, and a pair of removable lifting handles,wherein the container assembly has an internal cavity between theexterior surface and the interior surface and has a support structure inthe bottom of the container and the internal cavity is filled with afoam; a lid assembly pivotably having a lid hinge complementary to theat least one container hinge and attached to the at least one hinge onthe container assembly; a tub assembly that fits inside the containerassembly and having a base section, wherein the base section contains aplurality of passages that extend from a first end of the tub assemblyhaving a first turning manifold to a second end of the tub assembly, andopposite the first end, having a second turning manifold, and whereinthe tub assembly contains a combustion gas chamber positioned proximatethe second end of the tub assembly; wherein the plurality of passagescomprises a first group, a second group and a third group of parallelflow passages, wherein the first group of parallel flow passages directshot combustion gas byproducts from the combustion gas chamber s echo nto the first turning manifold, the second group of parallel flowpassages directs hot combustion gas byproducts from the first turningmanifold to the second turning manifold, and third group of parallelflow passages directs hot combustion gas byproducts from the secondturning manifold to an exit manifold.
 4. The portable heating device ofclaim 3, further comprising: wherein the container assembly has anintegrated shelf and the tub assembly has a tub shelf whereby the tubshelf rests on the integrated shelf to support the tub assembly when thetub assembly is filled with a liquid.
 5. The portable heating device ofclaim 4, further comprising: a removable screen positioned on the tubshelf.
 6. The portable heating device of claim 4, further comprising: aremovable wire tray.
 7. The portable heating device of claim 3, furthercomprising: molded threaded inserts included in the container assemblyand lid assembly in order to secure essential and optional componentsonto either the container assembly and lid assembly.
 8. The portableheating device of claim 3, further comprising: wherein the lid assemblyis filled with a foam and the lid assembly has an integrated lid handle,integrated lid support structure, integrated lid vent, and an integratedlid gasket track.
 9. The portable heating device of claim 3, furthercomprising: a burner box assembly secured to one end of the containerassembly.
 10. The portable heating device of claim 3, furthercomprising: an exhaust assembly position on one end of the containerassembly and including an exhaust tube, exhaust container gasket, anexhaust tub gasket, and an exhaust plate.